Hexagonal lattice geometry for Monte Carlo calculations

Abstract A method is proposed to treat a hexagonal lattice for a Monte Carlo calculation. The present method has a flexibility in geometry description and is particularly suitable for a vectorized code using the combinatorial geometry. Particles belonging to the symmetric cells with respect to a reference type cell can be simultaneously processed as if those belong to the reference cell in the transformed coordinate system. As a result, a length of vector increases much in particle tracking calculations. The calculational algorithm is simple and reduces the number of conditional IF statements in a program. This method has been implemented in a vectorized Monte Carlo code GMVP and assessed by solving two sample problems. The results were compared with those obtained by the collision probability method. The speedup by the vectorization is about a factor of 24 on the FACOM VP-2600 computer.